The present invention relates to a spine osteosynthesis device, in particular a clamp for stabilizing a cervical spine segment, such as the cervical vertebrae C1 and C2.
It is known that certain cervical segments are unstable owing in particular to fractures of cervical vertebrae resulting from accidents on the road or injuries undergone by the intervertebral connections such as the ligaments. Various devices for stabilizing the unstable vertebral segment have therefore been proposed which also permit reducing the time the patient spends in hospital and protecting his nervous system. A known arrangement consists in achieving the stabilization by means of wires binding two cervical vertebrae together. In other known arrangements, the stabilization is achieved by means of two elements hooking onto the vertebrae, interconnected by a screw threaded rod and tightened by nuts, or by means of vertebral screws.
These various techniques present the following drawbacks: first, the stability obtained is insufficient, since the wires are not necessarily tightened in their stable position on the vertebrae. The screw threaded rods interconnecting the hooks to form a clamp stabilizing the vertebral segment may gradually unscrew, since nothing opposes the gradual unscrewing of their tightening nuts. A second drawback resides in the difficulty of placing these devices in position owing to the very deep field of operation due to the flesh covering the vertebrae. A third drawback resides in the inconvenient size of the devices employing screws, hooks and clamps which also present serious neurological risks.
As concerns the wires, their obligatory passage behind the posterior elements of the cervical vertebrae is delicate and involves risks which are well noted in the literature. Further, as the surface of contact between the wires and the bone is small, the "butter cutting wire" phenomenon is frequently observed, and a steel wire has the particularity of easily breaking within a short period, whence a risk of a secondary instability or pseudoarthrosis.
The other implants existing on the market pose the problem of the difficulty of inserting them and often of their overall size and the reliability of the connection between implants.
Besides, the usual connection means between an osteosynthesis rod and spinal anchorage hooks or screws comprise screws, which are not easy to correctly put in place by the surgeon.